Kinetics and equilibrium studies on the uptake of Nd3+ by Zn–Al layered double hydroxide intercalated with triethylenetetramine-hexaacetic acid

Abstract

A Zn–Al layered double hydroxide intercalated with triethylenetetramine-hexaacetic acid (TTHA·Zn−Al LDH) was able to take up Nd3+ from an aqueous solution. To determine the reaction mechanism of this Nd3+ uptake by TTHA·Zn−Al LDH, we conducted kinetics and equilibrium studies. The uptake was more adequately described by the mass-transfer-controlled shrinking core model than the surface-reaction-controlled model. The apparent activation energy was 15.0 kJ mol−1, confirming that the reaction involved in the uptake of Nd3+ by TTHA·Zn−Al LDH proceeds under mass transfer control. This reaction could also be expressed by Langmuir-type adsorption, suggesting the formation of a chelate complex between Nd3+ and TTHA ions in the TTHA·Zn−Al LDH interlayer. The equilibrium adsorption constant was 2.6, and the maximum adsorption amount was 0.3 mmol g−1.